PROPELLER TIP CAVITATION SUPPRESSION USING SELECTIVE INTERMITTENT POLYMER INJECTIONS

WITH RECENT ADVANCES IN ACOUSTIC DETECTION TECHNIQUES, QUIETING OF SHIP PROPELLERS IS ESSENTIAL. WE PROPOSE HERE TO DELAY TIP VORTEX CAVITATION BY INJECTION OF LONG CHAIN DRAG REDUCING POLYMERS IN THE TIP VORTEX CORE AND THUS REDUCING THE TIP VORTEX INDUCED CAVITATION NOISE. FOR THIS TO BE EFFECTIVE, WITHOUT ANY DRAWBACKS ON PROPELLER PERFORMANCE, THE INJECTION HAS TO BE SELECTIVE: THE POLYMERS HAVE TO BE INTRODUCED ONLY IN THE VISCOUS CORE OF THE TIP VORTEX. THE INJECTION HAS ALSO TO BE ON AN AS NEEDED BASIS TO MINIMIZE POLYMER SOLUTION CONSUMPTION, AND TRANSPORT CONSTRAINTS ON THE VESSEL. THESE TWO OBJECTIVES COULD BE ACHIEVED IF THE INJECTION PORTS ARE WELL LOCATED ON THE BLADES AND IF A FEED BACK MECHANISM IS ESTABLISHED BETWEEN THE PROPELLER FLOW FIELD AND THE POLYMER SOLUTION INJECTION. WE PROPOSE TO INVESTIGATE THE FEASIBILITY OF THIS CONCEPT IN THE PHASE I EFFORT OF THIS PROPOSED RESEARCH PROGRAM. AN ACTUAL MODEL SCALE PROPELLER DESIGNED FOR A NAVY VESSEL WILL BE USED. ITS CHARACTERISTICS AND ITS CAVITATION INCEPTION CURVES WILL BE ESTABLISHED FOR A BASELINE. THEN THE PROPELLER WILL BE MODIFIED BY FITTING TWO OF ITS BLADES WITH FLUID INJECTION PORTS WHOSE POSITION WILL BE DETERMINED FROM THE VISUALIZATION OF THE FLOW AROUND THE UNMODIFIED PROPELLER. VARIOUS CONCENTRATIONS OF POLYMER SOLUTION INJECTIONS WILL THEN BE PERFORMED AND MODIFICATION OF THE CAVITATION INCEPTION CHARACTERISTICS SOUGHT. THE RESULTS WILL BE COMPARED WITH THE BASELINE TESTS AS WELL AS WITH PURE WATER AND WATER/GLYCERINE SOLUTION INJECTION IN THE SAME AMOUNTS. AS A RESULT, CRITERIA AND A PROCEDURE FOR PROPELLER DESIGN TO DELAY TIP VORTEX CAVITATION INCEPTION WILL BE ESTABLISHED. THESE WOULD BE REFINED IN PHASE II OF THE PROPOSED EFFORT.